Bipolar transistor having a low doped drift layer of crystalline SiC

Abstract

A bipolar transistor having at least a low doped drift layer ( 14 ) of crystalline SiC comprises at least one first layer ( 13 ) of a semi-conductor material having a wider energy gap between the conduction band and the valence band than an adjacent layer ( 14 ) of SiC.

What is claimed is:  
     
       1. A bipolar transistor having at least a low doped drift layer ( 7 ,  14 ) of crystalline SiC characterized in that it comprises: 
       at least one first layer ( 2 ,  12 ,  13 ,  15 ,  16 ,  19 ) of a semiconductor material having a wider energy gap between the conduction band and the valence band than an adjacent layer of SiC, wherein the emitter ( 2 ,  13 ,  15 ) of the transistor is one said first layer;  
       a continuous base layer ( 6 ) doped according to a first conductivity type and physically separating the emitter ( 2 ) and the collector ( 4 ) of the transistor, which are doped according to an opposite, second conductivity type; and  
       an energy barrier means ( 11 ,  12 ) is arranged next to an electrode, making contact to the base layer, for introducing an energy barrier for minority charge carriers injected into the base layer from the emitter for reducing recombination of such minority charge carriers at the base contact electrode.  
     
     
       2. A transistor according to claim  1 , characterized in that said means are formed by a sub-layer ( 11 ) of said base layer ( 6 ) located next to said contact electrode ( 5 ) and having a higher doping concentration of said first. conductivity type than the rest of the base layer. 
     
     
       3. A transistor according to claim  1 , characterized in that said means are formed by the arrangement of one said first layer ( 12 ) next to the base layer ( 6 ) for forming the base layer contact electrode and which is doped according to the first conductivity type. 
     
     
       4. A transistor according to any of claim  3 , characterized in that said first layer ( 2 ,  12 ,  13 ,  15 ,  16 ,  19 ) has a group  3 B-Nitride as major component. 
     
     
       5. A transistor according to claim  4 , characterized in that said first layer ( 2 ,  12 ,  13 ,  15 ,  16 ,  19 ) has Al x Ga 1−x N as said major component. 
     
     
       6. A transistor according to claim  5 , characterized in that x is less than 0.2. 
     
     
       7. A transistor according to claim  5 , characterized in that the junction ( 9 ) between said first layer and a layer of SiC adjacent thereto is graded with x decreasing in the direction away from said adjacent layer of SiC. 
     
     
       8. A transistor according to any of claim  5 , characterized in that said first layer ( 2 ,  12 ,  13 ,  15 ,  16 ,  19 ) comprises a thin sub-layer of AIN forming an interface between said first layer and an adjacent layer of SiC. 
     
     
       9. A transistor according to any of claim  1 , characterized in that said first layer is made of crystalline SiC of another polytype than an adjacent layer of SiC. 
     
     
       10. A use of a transistor according to any of claim  1  for high power and/or high voltage applications. 
     
     
       11. A use according to claim  10 , characterized in that it is designed to be able to hold a voltage higher than 5 kV when reversed biased. 
     
     
       12. A bipolar transistor having at least a low doped drift layer ( 7 ,  14 ) of crystalline SiC characterized in that it comprises: 
       at least one first layer ( 2 .  12 ,  13 ,  15 ,  16 ,  19 ) of a semiconductor material having a wider energy gap between the conduction band and the valence band than an adjacent layer of SiC; and  
       the base of the transistor is formed by a grid ( 16 ,  19 ) doped according to a first conductivity type and buried in the drift layer ( 14 ) doped according to an opposite, second conductivity type while leaving drift layer regions ( 18 ) between adjacent grid bars ( 17 ), wherein the emitter ( 13 ) and the collector ( 15 ) of the transistor are also doped according to said second conductivity type.  
     
     
       13. A transistor according to claim  12 , characterized in that it comprises two base grids, one ( 16 ) arranged close to the emitter and the other ( 19 ) close to the collector, so that the transistor is bidirectional with respect to current conduction and turn-off capabilities and the base grid closest to the emitter in the respective type of operation of the transistor is arranged to be used to control the transistor. 
     
     
       14. A transistor according to claim  12 , characterized in that the base grid ( 16 ,  19 ) is one said first layer. 
     
     
       15. A transistor according to claim  14 , characterized in that both the base grid ( 16 ,  19 ) and the emitter ( 13 ,  15 ) are a said first layer of a material having a wider energy gap between the conduction band and the valence band than the SiC of the drift layer. 
     
     
       16. A transistor according to any of claims  12 , characterized in that the different grid bars extend vertically to the surface ( 17 ,  21 ) of the transistor and emitter portions ( 13 ) are arranged on regions of said surface between adjacent grid bar surfaces ( 22 ). 
     
     
       17. A transistor according to claim  12 , characterized in that the lateral distance between adjacent grid bars ( 17 ) in the drift layer ( 14 ) is selected so that the drift layer regions ( 18 ) separating adjacent grid bars will be completely depleted when a voltage exceeding 200 V is applied in the reverse direction between the emitter and the collector of the transistor.